This application claims the benefit of the filing date as provided in 35 U.S.C. 119 of United Kingdom patent application number GB 9910026.5 filed on Apr. 30, 1999, the disclosures of which are incorporated herein by reference.
The present invention relates to congestion in a telecommunications network and more particularly to alleviating congestion during the routing of signalling information between signalling points of a telecommunications network.
In a modern telecommunications network, a considerable amount of signalling information is continually being exchanged between signalling points of the network. Examples of signalling points are network switches, databases, etc. The actual signalling information being exchanged may be associated with a specific telephone call, e.g. relating to call set-up or termination, or may relate to network management functions. Complex protocols have been created to deal with the exchange of signalling information. In particular, Signalling System no.7 (SS7) defines (subject to certain national/regional variations) a suite of protocol parts (or levels) capable of dealing with modern network signalling demands.
FIG. 1 illustrates schematically the xe2x80x9cstructurexe2x80x9d of SS7 (it will be appreciated that the SS7 parts are generally implemented by means of software running on computer processors). On top of the SS7 stack sit the user and application parts which are the entities which make use of and provide signalling information. For example, an ISDN User Part (ISUP) controls the setting up and control of inter-exchange connections for subscriber calls whilst a Mobile Application Part (MAP) handles database queries in a mobile network (e.g. to determine the current location of a mobile subscriber).
At the bottom of the SS7 is the Message Transfer Part (MTP) which in fact comprises three distinct levels. Level 1 defines the physical, electrical, and functional characteristics of a digital signalling link. MTP level 1 has a number of different possible forms including the European standard E.1 (2048 kb/s and 32 64 kb/s channels). MTP level 2 takes care of the accurate end-to-end transmission of messages across a chosen signalling link, whilst MTP level 3 handles the routing of signalling messages between neighbouring signalling links based upon information received from higher SS7 a levels concerning the final destination of a signalling message. MTP level 3 handles inter alia re-routing of messages away from failed or congested signalling links.
Routing by MTP level 3 is carried out based on a destination signalling point and subsystem number (SSN), provided to the MTP by a higher SS7 layer. In particular, for the Transaction Capabilities Application Part TCAP (which handles database queries for the MAP, INAP etc) a Signalling Connection and Control Part (SCCP) generates the destination signalling point and subsystem number using a process termed xe2x80x9cGlobal Title translationxe2x80x9d. The SCCP typically carries out a Global Title translation on a Global Title (GT), which may be a dialled Intelligent Network (IN) service number, e.g. an 800 number, a subscriber identification number or the like, using a Global Title Routing Case (GTRC) table. This table contains a mapping between GT series and GTRCs (a GTRC typically being one of an ordered series of numbers). A further GTRC translation is then performed to map the determined GTRC to an associated primary destination signalling point (and subsystem number). The destination signalling point is in some cases referred to as a xe2x80x9cDestination Point Codexe2x80x9d (DPC).
A Global Title routing case defines, by way of the destination signalling point, the route via which signalling information is transmitted. Especially during peak calling times, certain routes may become congested with large volumes of signalling traffic. Indeed, it is often the case that when a call is initiated, the primary destination signalling point generated by the GT and GTRC translations associated with the call, is unavailable. In such a situation (and following the broadcast of a congestion message from a given signalling point to neighbouring signalling points), a secondary destination signalling point, defined as a back-up for the primary destination signalling point, is used to route the signalling information. This procedure is described in ITU-T Recommendation Q.714 (Chapter 5).
It will be appreciated that the secondary destination signalling point handles overflow signalling information which the primary destination signalling point is unable to handle. It will also be appreciated that when overflow occurs, the processor(s) at the primary destination signalling point will be working at maximum capacity whilst those at the secondary destination signalling point may be working well below that maximum capacity. It may also happen that the secondary destination signalling point subsequently becomes congested, requiring the transfer of signalling information back to the primary destination signalling point (if the primary signalling point remains congested, a further switch back to the secondary point may occur, and so on). This switching back and forward between the primary and secondary destination signalling points may result in the loss of signalling information.
It is an object of the present invention to overcome or at least mitigate the disadvantages outlined in the preceding paragraph. In particular, it is an object of the present invention to avoid or mitigate congestion associated with signalling traffic routed by the Signalling Connection and Control Part. It is a further object of the present invention to provide means by which possible congestion at a signalling point can be predicted, thereby enabling signalling traffic to be diverted away from that signalling point before congestion occurs.
These and other objects are achieved in a first aspect of the invention by defining peak periods during which heavy signalling traffic is expected. During these peak periods, a proportion of the Global Titles normally allocated to a given destination signalling point are automatically reallocated to an alternative destination signalling point. The peak periods are defined on the basis of the history of congestion notification messages issued by the given signalling point.
According to a first aspect of the present invention there is provided a method of routing signalling information at a signalling point of a telecommunications network, the method comprising:
providing a Global Title Routing Case (GTRC) table mapping Global Titles to GTRCs;
allocating to a set of GTRCs a primary and a secondary destination signalling point;
defining at least one time period on the basis of a history of congestion notification messages issued by said primary destination signalling point;
swapping said primary and secondary destination signalling points for a fraction of said set of GTRCs for the duration of said at least one time period;
for a signalling transfer request at the signalling point, mapping the Global Title associated with the request to a GTRC using the GTRC table; and
determining the destination signalling point to be used for the request in dependence upon the primary and secondary destination signalling points allocated to the mapped GTRC and signalling point availability.
By carefully selecting said time period(s) to correspond to known peak signalling traffic periods, embodiments of the present invention automatically divert traffic away from the primary destination signalling point without having to wait until congestion of the primary destination signalling point actually occurs. The resulting load sharing reduces the risk of congestion at the primary and secondary destination signalling points. This results in a more optimal use of processor power at the destination signalling points and also reduces the need to transfer signalling traffic from a congested route to a back-up route. Furthermore, as the maximum volume of signalling traffic through a given signalling point is likely to be reduced, the maximum processing power specified for the point (i.e. its xe2x80x9cdimensioningxe2x80x9d) can be reduced, resulting in a considerable cost saving.
It will be understood that the term xe2x80x9cGlobal Titlesxe2x80x9d encompasses, but is not limited to, calling and called party telephone numbers, subscriber identity number, mobile identification number, and the like. The GTRC table may map Global Titles to GTRCs using Global Title series, i.e. where Global Titles are grouped into series and each series is mapped to a corresponding GTRC.
Preferably, said destination signalling points are Destination Point Codes (DPC) or the like, which DPCs identify signalling points designated to receive the signalling information.
Preferably, at least one time period is defined for every 24 hours period of operation. More preferably, said first period(s) corresponds to a relatively high usage period.
Preferably, congestion notification messages are broadcast by signalling points in the network, when the points become congested. These messages are monitored at other points of the network to create a congestion history for the sending signalling points. On the basis of these histories, a signalling point defines said time period(s). The congestion notification messages may contain a congestion level which may additionally be used by a receiving signalling point to define said time period(s).
Preferably, the method of the present invention is employed in a Signalling Connection and Control Part (SCCP) of a Signalling System no.7 (SS7) network. The congestion notification messages may be SCCP/Subsystem Congested (SSC) messages.
Preferably, said time period(s) is defined dynamically so that they may be moved, or their duration changed, to reflect changing patterns in network traffic. This process may be automatic, or semi-automatic.
The time period(s) may be defined additionally using query messages sent from said signalling point to said primary destination signalling point, where the primary destination signalling point responds to receipt of the query by returning an answer message to the signalling point. Based upon the delay between transmitting the query and receiving the answer, the signalling point is able to estimate the congestion level at the primary destination point and over the intervening signalling link. If such queries are sent at regular intervals, the signalling point is able to supplement the information obtained from the congestion notification messages. In a network employing SCCP, the query message is known as Subsystem Test (SST) whilst the answer message is know as Subsystem Allowed (SSA).
According to a second aspect of the present invention there is provided apparatus for routing signalling information at a signalling point of a telecommunications network, the apparatus comprising:
first memory means for storing a Global Title Routing Case (GTRC) table mapping Global Titles to GTRCs;
second memory means for storing for a set of GTRCs a primary and a secondary destination signalling point;
first signal processing means for swapping said primary and secondary destination signalling points for the duration of a time period defined on the basis of a history of congestion notification messages issued by the primary destination signalling point; and
second signal processor means arranged to receive signalling transfer requests and to determine the destination signalling point to be used for the request in dependence upon the primary and secondary destination signalling points allocated to the mapped GTRC and signalling point availability.
Preferably, the apparatus comprises intelligent processing means arranged to respond to changing signalling traffic levels over time, by adapting the duration and position of said time period.
According to a third aspect of the present invention there is provided a Signalling Connection and Control Part (SCCP) for use in a Signalling System no.7 signalling network, the SCCP comprising:
a Global Title Routing Case (GTRC) table mapping Global Titles to GTRCs;
a primary and a secondary destination signalling point allocated to a set of GTRCs;
a definition of at least one time period, said definition being made on the basis of a history of congestion notification messages issued by the primary destination signalling point;
means arranged to swap said primary and secondary destination signalling points for a fraction of said set of GTRCs for the duration of said time period;
means for mapping a Global Title, associated with a signalling transfer request received at the signalling point, to a GTRC using the GTRC table; and
means for determining the destination signalling point to be used for the request in dependence upon the primary and secondary destination signalling points allocated to the mapped GTRC and signalling point availability.
According to a fourth aspect of the present invention there is provided a method of determining congestion at a destination signalling point of a telecommunications network, the method comprising:
sending an echo request message from a signalling point to said destination signalling point;
in response to receipt of said echo request message at the destination signalling point, returning to said signalling point an answer message; and
determining at the signalling point the delay between sending the echo request message and receiving the answer message, wherein said delay provides an indication of the congestion level at said destination signalling point.
Preferably, said destination signalling point is one of a set of destination signalling points polled by the signalling point. This set may correspond to those destination signalling points in the network where congestion is likely to occur.
Where said signalling point and said destination signalling point(s) use SCCP, the echo request message may be an SCCP/Subsystem Status Test (SST) message whilst the answer message may be a Subsystem Status Allowed (SSA) message. It is noted that this proposal represents a new use for SSC and SSA messages which are normally used for determining the operational status of a remote network node.
Embodiments of the present invention may use a determined echo response delay to dynamically allocate and/or reallocate signalling traffic to destination signalling points, e.g. signalling traffic may be switched from a primary destination signalling point to a secondary destination signalling point if the primary destination signalling point is observed to be becoming congested.
In other embodiments of the invention, echo response delays, or congestion levels derived therefrom, for a destination signalling point are recorded over a period of time and, using this history, peak signalling traffic periods are defined. During such peak periods, signalling traffic may be automatically transferred from the destination signalling point to some other secondary destination signalling point. These periods may be dynamically redefined if the pattern of signalling traffic within the network (and as represented in the congestion histories) changes.
Embodiments of the fourth aspect of the invention may comprise the steps of:
providing a Global Title Routing Case (GTRC) table mapping Global Titles to GTRCs;
allocating to each GTRC a primary and a secondary destination signalling point;
swapping said primary and secondary destination signalling points for a fraction of said GTRCs when the primary destination signalling point is nearing congestion or is predicted to be nearing congestion;
for a signalling request at the signalling point, mapping the Global Title associated with the request to a GTRC using the GTRC table; and
determining the destination signalling point to be used for the request in dependence upon the primary and secondary destination signalling points allocated to the mapped GTRC.
According to a fifth aspect of the present invention there is provided apparatus for determining congestion at a destination signalling point of a telecommunications network, the apparatus comprising:
transmission means for sending an echo request message from a signalling point to a destination signalling point;
automatic response means for returning to said signalling point an answer message in response to receipt of said echo request message; and
processing means at the signalling point for determining the delay between sending the echo request message and receiving the answer message, wherein said delay provides an indication of the congestion level at said destination signalling point.